A fad diet is a trendy, often highly restrictive eating plan promoted as a quick solution for weight loss or health improvement, typically lacking scientific evidence or long-term sustainability.
These diets often emphasize specific foods, extreme calorie cuts, or the elimination of entire food groups (e.g., keto, paleo, grapefruit diet, or juice cleanses) while promising rapid results. They may lead to short-term weight loss due to calorie restriction but often fail to provide balanced nutrition, can cause nutrient deficiencies, and are difficult to maintain, leading to weight regain.